Project Summary Dr. Shea's career goal is to become an independent physician-scientist and a leader in the understanding of fibrotic lung diseases. He completed his clinical training in Pulmonary and Critical Care Medicine in the Harvard Combined Fellowship Program, and he has been studying lung fibrosis in Dr. Andrew Tager's laboratory at Massachusetts General Hospital for the past three and a half years. Their work together has led to exciting discoveries on the roles of the lipid mediators, lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P), in lung injury and fibrosis. This work has been published in Nature Medicine and the American Journal of Respiratory Cell and Molecular Biology. Dr. Shea has been selected to present his research on S1P in lung fibrosis at several international conferences, and he was awarded first prize in the basic science category at the Sixth Annual Respiratory Disease Young Investigators' Forum. Dr. Shea has an ideal environment in which to perform the research outlined in this proposal and pursue his career goals. He will continue to be mentored by Dr. Tager, an exceptional scientist who has provided Dr. Shea with outstanding mentorship thus far in his career, and who is genuinely committed to fostering Dr. Shea's growth and independence as a scientist. Dr. Shea has access to all of the physical and intellectual resources of the MGH Center for Immunology and Inflammatory Diseases (CIID) and Pulmonary and Critical Care Unit (PCCU), and the full support of the CIID, the PCCU, and the MGH Department of Medicine. He has also assembled a formidable advisory committee composed of highly successful scientists who are committed to assisting Dr. Shea in his research endeavors and career development. We have found that antagonism of the S1P receptor, S1P1, dramatically worsened pulmonary vascular leak and fibrosis after bleomycin challenge in mice. Our overall hypotheses are that (1) S1P-S1P1 signaling on endothelial cells protects against vascular leak after lung injury and (2) attenuating vascular leak protects against injury-induced lung fibrosis by limiting the extravasation of plasma clotting factors, and the subsequent activation of thrombin/PAR-1 signaling, within the airspaces. The first aim of this proposal is to determine the importance of endothelial S1P-S1P1 signaling to the regulation of lung injury and fibrosis, by assessing the susceptibility of inducible, endothelial-specific S1P1-deficient mice to vascular leak and fibrosis after bleomycin lung injury. The second aim of this proposal is to determine the mechanistic link between vascular leak and fibrosis, by investigating whether the ability of S1P1 antagonism to exacerbate the fibrotic response to bleomycin lung injury is abrogated in PAR-1 deficient mice. The third aim of this proposal is to determine whether augmentation of S1P levels can protect against lung injury and fibrosis, which we will accomplish by delivering an adenovirus gene transfer vector expressing the S1P-producing enzyme, sphingosine kinase 1, to the lungs of mice, then determining their susceptibility to vascular leak and fibrosis after bleomycin lung injury.